1. Technical Field
The present invention relates to a lens system that reduces or eliminates ghost images.
2. Related Background Art
Digital imaging cameras use solid-state image sensors such as CCD or CMOS imagers to convert optical images into electronic signals. As the resolution of the imagers increases, there is a continuous need for optical lenses with increased performance. An important characteristic of the lens is the ability to produce high-resolution images across a wide field of view. Another important characteristic is to produce such high-resolution images using a lens that is of a compact size. Another important characteristic is to produce images that are free of secondary ghost images caused by double reflections within the imaging system including the surfaces of the internal lens elements, any filters and the cover glass of the imaging sensor. This requirement can be especially important when the sun or other bright source is included in the image field of view. The lenses are increasingly being incorporated into a variety of electronic devices including mobile phones, cameras, sports cameras, computers and computer peripherals. Incorporation of the lenses into new devices also places new environmental performance requirements upon the lens. The lens must be compact and light, to be used in portable devices, and must maintain the high performance characteristics.
A common fault of wide-angle lens is the appearance of secondary images. Wide-angle lenses are more prone to have ghost reflections. Every transition of light ray across a material boundary where the materials have different refractive indices can produce a partial reflection of the light. In a typical digital imaging system these transitions are between air and the lens material and occur at every lens boundary as well as at the surfaces of filters and imager cover glasses. When these secondary reflections form an image on the image sensor a ghost image is produced. Current technology to reduce or eliminate ghost images includes the design of the lens, the material used for the lens and other elements in the imaging system and coatings that are applied to the lenses and other elements. There is still a need for improved performance especially in cases where very bright objects are included in the field of view of the lens. It is an object of this invention to provide wide-angle lenses with reduced ghost reflections and thus providing an improved image quality over a wide range of lighting conditions including those having the sun within the field of view of the lens. It is also an objective that the lens design is compact such that it can be fit into small electronic devices.